In operations in which two workpieces are joined together, a well known method of joining the two workpieces is to form mating profiles in each of the workpieces, i.e., a tenon and a recess, which are sized to fit together as a mating pair. This joining technique is often used in the manufacture and assembly of workpieces such as doors, in general, and panel doors, in particular, such as those used in cabinetry and decorative doors. In door making, it is preferred to form tenons in the support rails of the door in an extended length. Such extended length tenons provide increased support for the support joints of the door, therefore creating a more sturdy door. A door assembled using support rails that have conventional length tenons tends to sag and is considered to be less sturdy and of inferior quality.
As is well known in the art, when it is desired to cut a profile with a recess or a corresponding tenon into the edge of a workpiece, a pair of rotating bits, such as a molding bit and a coping bit, are provided, each of which typically include two cutter elements fixed onto a drive shaft. A profile has an aesthetically pleasing shaped surface and functional aspects such as a tenon or a recess and is formed into the end of a workpiece. The edge of the workpiece to be formed is moved laterally into contact with the rotating bits. If a recess is to be formed into the workpiece, typically a molding bit that includes two cutter members having a thickness corresponding to the desired thickness of the recess, is used. Similarly, if a tenon is to be formed into the workpiece, typically a coping bit that includes two cutter members fixed thereon at a spacing corresponding to the thickness of the tenon to be formed is used so that the edge of the workpiece is cut away by the cutter elements above and below the portion that becomes the tenon.
With molding and coping bits, it is possible to form recesses and tenons, respectively, of varying thicknesses. Spacer members of varying sizes may be removably mounted between the cutting members to create the desired thickness.
However, with the above-described pair of rotating bits, it is not possible to form tenons of an extended length because the centrally located drive shaft of the coping bit is an obstruction that limits the distance that the edge of a workpiece may extend across the surface of the cutters. Thus, a tenon formed using a coping bit with two cutters is limited in length.
It is also known to use a coping bit having a single cutter member mounted onto a drive shaft to form a tenon or a recess in a workpiece, respectively. When a rotating bit of this type is used, two separate cutting operations must be used to form the profile having a tenon in the workpiece because the rotating bit only has a single cutter member. A single cutter coping bit may be used when forming an extended tenon because there is no central bearing or other obstruction on the cutter member thereby leaving a flat unobstructed planar surface for the edge of the workpiece to extend across while one side of the tenon is being cut. It is possible to form profiles of varying thickness using a single cutter rotating bit because each side of the profile is formed in a separate cutting operation.
However, when using a coping bit having a single cutter, which requires two separate cutting operations to form a tenon, often alignment problems arise, especially when tenons are cut into many workpieces. For example, when assembling a door, tenons are cut along rails that form the top, bottom and intermediate frames of the door. With a coping bit having a single cutter, a single cut is made along the end of the workpiece to cut one face of the tenon needed and then a second cut is made along the other side of the workpiece to cut the other face of the same tenon needed on the end of the workpiece. If at any time during either one of these cutting operations, the workpiece moves slightly or the craftsman applies a slightly different pressure to the workpiece being cut, the tenon will not be evenly cut and alignment problems, i.e., problems with the tenons and recesses of the workpieces fitting together, will arise when trying to assemble the workpieces of the panel door. In addition, any variations in thickness of the workpiece being cut introduce a problem when using a coping bit having a single cutter because the sides of the workpiece are used as a reference when cutting with a coping bit of this type. As such, any variation in workpiece thickness will cause the craftsman to cut the tenon unevenly and will create an alignment problem when trying to fit the cut tenon into a matching recess. The risk of creating alignment problems is present for every workpiece cut with a coping bit have a single cutter.
Further, it is often the situation that a person using a pair of rotating bits will want to form recesses, conventional length tenons and extended length tenons all in the same project. For example, when making a door, it is usually necessary to form recesses, conventional length tenons and extended length tenons to assemble a sturdy, secure door. However, as described hereinabove, the pair of rotating bits with two cutters is unable to form extended tenons into a workpiece and the pair of rotating bits with a single cutter is difficult to use without experiencing alignment problems when attempting to assemble the finished product, as described in greater detail above.